Plug-in hybrid electric vehicles (PHEVs) include a traction battery to store electric power used by a traction motor to propel the vehicle. The electric power may be provided by an external power source, such as the power grid, or an on-board power source, such as a fuel cell or internal combustion engine. In some vehicle architectures, the on-board power source may provide torque to the vehicle wheels alone or in combination with the traction motor, while in other architectures the on-board power source is only used to provide electric power to the battery and/or traction motor. The vehicle operating strategy that determine whether to power the vehicle using the traction battery, second power source, or both, is typically determined by the manufacturer during design and development to achieve desired fuel economy, vehicle performance, and maintain the traction battery within desired operating parameters, for example. While drivers may be provided the option to operate in an electric only, engine only, or various types of hybrid operating modes, these modes are generally designed to achieve the best fuel economy within the constraints imposed by the selected operating mode.